1. Field of the Invention
The present invention relates to a focusing device for moving a lens of a small camera by driving a motor to control a focus.
2. Description of the Related Art
Such a kind of conventional technology is disclosed in the Patent Document 1. In the technology disclosed in Patent Document 1 (see Japanese Unexamined Patent Application Publication No. 2002-51524 (Paragraph Numbers 0058 and 0059 and FIG. 7) and corresponding U.S. Unexamined Patent Application Publication No. 2003/0178911A1), a pin is formed in a magnet that forms a rotor of a hollow motor and engages the above-described pin with a lens holder that holds a lens. The lens holder and a main body are connected to each other in a screw-shaped guide groove.
According to the conventional technology, when the rotor, that is, a magnet is rotated by driving the hollow motor, the lens holder rotates through the pin of the magnet. That is, the lens held in the lens holder proceeds so as to protrude from the main body or recedes so as to be received in the main body. Thus, the lens moves in an optical-axis direction to control the focus.
It has been desired to rapidly move the lens from a predetermined stand-by position, for example, an accommodating position of the main body to a minute focusing region and to minutely move the lens in the direction of the optical direction in the minute focusing region.
However, according to the above-described conventional technology, since the lens holder that holds the lens moves while rotating along the screw-shaped guide groove, it take long time for the lens to move from the reception position to the minute focusing region. Thus, it is not possible to satisfy the above-described desire.
Also, when the pitch of the guide groove is set to be large in the conventional technology, it is possible to secure a large amount of movement of the lens holder with respect to the number of rotations of the lens holder, that is, a large amount of movement of the lens such that it is possible to rapidly move the lens from the reception position to the minute focusing region. However, when the pitch of the guide groove is set to be large, it is not possible to realize minute motion such as focusing the lens in the minute focusing region, that is, to perform minute control. Thus, such a structure cannot be mentioned as practical.
When it is considered that the lens rapidly moves through a cam groove, a member for forming the cam groove is necessary in addition to a protrusion engaged with the cam groove such that the entire structure becomes complicated to increase the manufacturing cost.